1. Field of the Invention
The present invention relates to a flat display device having a thin display unit of a liquid crystal display type, a plasma display type, a rear projection display type or other display type. In particular, the present invention relates to a flat display device equipped with a rotation drive mechanism for rotating the display unit in the horizontal direction.
2. Description of Related Art
Conventionally, there is a display device equipped with a rotation drive mechanism for driving the display unit that displays reproduced pictures, in the horizontal direction by transmitting a driving force of a motor. Some examples of the rotation drive mechanism for a display device having a CRT as the display unit are disclosed in Japanese Utility Model No. 63-124775-A (a first document), Japanese Utility Model No. 03-042186-A (a second document), and JP-A-H04-061575 (a third document), for example.
In addition, as disclosed in JP-A-2004-304679 (a fourth document) for example, there is another example of the rotation drive mechanism for a flat display device having a thin display unit of a liquid crystal display type, a plasma display type, a rear projection display type or other display type.
According to the second document, the rotation drive mechanism has a structure in which an electromagnetic clutch is used and controlled in accordance with a load current of a drive motor under operation so that the rotation operation is stopped or controlled appropriately when the display unit touches an obstacle during the rotation operation. More specifically, when display unit touches an obstacle, the load current of the drive motor increases. Then, the contact between the display unit and the obstacle is detected from the load current, and the electromagnetic clutch is disconnected so that the rotation of the display unit is stopped.
According to the third document, the rotation drive mechanism uses a stepping motor that can obtain low rotation speed and high torque so as to secure a torque necessary for rotating a large display device instead of using a small DC motor having small torque and a power transmission gear having a high gear ratio. Since the stepping motor is used, the gear ratio of the power transmission gear can be reduced so that a structure thereof can be simplified. Thus, a structure of the rotation drive mechanism can be simplified.
According to the fourth document, the rotation drive mechanism includes a stepping motor, and a display unit of a flat display device can be rotated in the horizontal direction as well as in the tilt direction.
If the above-mentioned rotation drive mechanism is used for a flat display device, and if the flat display device is placed on a floor or the like, the entire device may be swayed when the rotation drive mechanism drives the display unit in the horizontal direction at a start or a stop operation of the rotation because of a high position of a barycenter of the device. In particular, the display unit may be swayed largely when the rotation drive mechanism stops the display unit just after starting the rotation thereof in the horizontal direction.
This swaying may be caused by an influence of inertia or the like, and the above-mentioned third document teaches a method for preventing the swaying mechanically by disposing a flat spring in a gap at a periphery of an upper portion of a rotation shaft. However, there is a limitation in preventing the swaying that occurs in the display unit by the mechanical method.